An interferometer generates an interference pattern when two waves of the same frequency constructively or destructively add. Generally, interferometers measure the variation of intensity at a function of path difference in the interferometer's arms. A common type of interferometer is termed a Michelson interferometer. Typically, this type of interferometer uses a monochromatic source such as a laser. Two mirrors define two arms of the interferometer with respect to a third semitransparent mirror or beam splitter. When the two paths differ by a whole number of wavelengths, for example, there is constructive interference at a detector.
Another type of interferometers is a Mach Zehnder interferometer. This interferometer uses two beam splitters and two completely reflective mirrors. The source beam is split and the two resulting waves travel along separate arms. Still another interferometer configuration is termed a Sagnac interferometer. In this configuration, two beams follow different paths around a ring, typically constructed from a series of mirrors. At the return point of the light, it exits to generate an interference pattern at the detector.
A common application for interferometers is Fourier transform spectroscopy. Time-domain measurements are made of a broadband optical signal. By modulating the path length of one of the arms of the interferometer, a spectrum can be reconstructed using a reverse Fourier transform of the temporal response of the detector. Commonly, Fourier transform spectroscopy is performed at infrared, including near infrared, wavelengths although other wavelengths stretching into the visible bands are also used.
In more detail, IR absorption spectroscopy is the basic technology used to differentiate detailed molecular structure and can be applied even when mixtures are present. Because the technique is quite mature, and used by a very large number of researchers in addition to routine process control, there are many commercially used chemical search programs for automated chemical identification and ranking. Generally, the IR absorption system offers extreme specificity, good sensitivity, and builds on established models for predicting performance using available spectral libraries of compounds.
At the same time, MicroElectroMechanical Systems (MEMS) fabrication techniques have been perfected. For example, a number of techniques have been demonstrated for the creation of out-of-plane MEMS structures. These fabrication processes require means for erecting the structures, holding them in the erected position, and doing so with adequate accuracy to achieve the required system performance. For example, Yi et al., in U.S. Pat. No. 6,166,478, has described a microelectromechanical system that includes at least two hinged flaps, each having a different amount of Permalloy or other magnetic material. The flaps are hinged at an angle to each other, and can be rotated off plane when placed in an increasing magnetic field. The flaps are raised asynchronously, at different times, due to the different amounts of Permalloy used in the flaps. As they are raised, the flaps interact with each other and become interlocked. Fan, in U.S. Pat. No. 6,556,741 and U.S. Pat. No. 6,600,850, describes torsional hinges and a notched latching mechanism for out-of-plane MEMS structures.